The art and science of present day superalloys has undergone a very interesting history. From a practical view point, the early alloys of Elwood Haynes (circa 1905) constituted the basic origin of the modern cobalt-chromium superalloys, under the trademark "STELLITE". His alloys were originally covered by U.S. Pat. Nos. 873,745, 1,057,423 and others. About thirty years later, Charles H. Prange invented a somewhat similar cobalt-base alloy for use as cast metal dentures and prosthetics as disclosed in U.S. Pat. Nos. 1,958,446, 2,135,600 and others. Prange's alloy is known in the art as "Vitallium" alloy.
The development of gas turbine engines in the early 1940's, created a need for materials capable of withstanding high forces at high temperatures. U.S. Pat. No. 2,381,459 discloses the discovery of Prange's "Vitallium" alloys modified for use as gas turbine engine components. The major commercial alloy developed from the original "Vitallium" alloy is STELLITE.RTM. alloy No. 21 essentially as disclosed in U.S. Pat. No. 2,381,459 and 2,293,206 to meet high temperature demands in industry. The basic composition of alloy 21 has been modified and further developed into many other commercial superalloys because of the need for improvements to meet more severe conditions required in gas turbine engines and other modern uses.
There have been hundreds of cobalt-and-nickel base alloys invented and developed for these uses. This vital need continues today. From a practical view, even minor advances in more sophisticated engines are in most cases principally limited by the availability of materials capable of withstanding the new, and more severe, demands.
A careful study of the many valuable alloys that are invented reveals that a subtle, seemingly ineffective, modification of existing alloys may provide a new and useful alloy suited for certain specific uses. Such modifications include, for example, (1) a new maximum limit of a known impurity; (2) a new range of an effective element; (3) a critical ratio of certain elements already specified; and the like. Thus, in superalloy developments valuable advances are not necessarily made by great strides of new science or art, but rather by small unexpected, but effective increments.
People skilled in the superalloy arts are constantly reviewing the known problems and evaluating the known alloys. In spite of this, many problems remain unsolved for several decades until an improved alloy must be invented to solve the problem. Such improvement, however seemingly simple in hindsight, cannot be assumed to be obvious or mere extention of known art.